1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method and a computer readable memory medium, and more particularly to an image data encoding or decoding process for image protection (protection of intellectual property right (for example copyright)).
2. Related Background Art
For encoding a moving image, there have been known an intraframe encoding method such as Motion JPEG (Joint Photographic Coding Experts Group) and an encoding method of digital video, and a method based on interframe prediction encoding such as H.261, H.263, MPEG (Moving Picture Coding Experts Group)-1 or MPEG-2. These encoding methods are recognized as international standards by ISO (International Organization for Standardization) or ITU (International Telecommunication Union). The former one, executing encoding independently for each frame and enabling easy frame management, is best suited for editing the moving image or for an apparatus requiring special reproduction. On the other hand, the latter one, relying on the interframe prediction, are featured by a high encoding efficiency.
Also MPEG-4 is now in the course of international standardization as a general-purpose next-generation multi-media encoding standard usable in various areas such as computer, broadcasting, communication etc.
With the spreading of the aforementioned digital encoding standards, the issue of copyright protection is strongly requested from the contents industries. Stated differently, the issue is that the good contents cannot be safely provided in a standard which cannot guarantee the sufficient protection of the copyright.
Therefore, in order to protect the copyright of a part of the moving image, there is conceived a method of temporarily suspending the decoding of the moving image so as not to reproduce a part thereof. In consideration of the image right or copyright of the moving image, the method suspends the decoding of a portion relating to such rights and re-starts the decoding when such portion is over.
There is however encountered the following drawback.
For encoding a moving image, there is generally employed an encoding method utilizing interframe correlation, as represented by H.261, H.263, MPEG-1, MPEG-2 or MPEG-4 mentioned in the foregoing, In these encoding methods, the encoding is basically executed by referring to a frame preceding in time or preceding and following frames, and accordingly executing movement compensation.
FIG. 1 shows the mode of reproduction in H.261, H.263 etc., wherein Ix indicates a frame for executing intraframe encoding and Px indicates a frame for executing interframe encoding. In FIG. 1, time indicates the direction of lapse of time. In security, a black zone indicates the period in which the decoding is interrupted for image protection (protection of intellectual property right (for example copyright)), while code indicates the arrangement of images in the order of encoding process, and display indicates the arrangement of images in the order of display.
It is now assumed that the decoding is interrupted in a period from P4 to P7 for the purpose of security (image protection (protection of intellectual property right (for example copyright))). The decoding of the moving image is stopped at P3 and the image is no longer displayed until the decoding is re-started. Since the writing of the encoded data into the buffer is also stopped simultaneous with the interruption of decoding, the encoded data from P4 to P7 are discarded. Therefore, when the decoding is re-started from P8, the decoding thereafter cannot be executed in normal manner since the data of P7 to be referred to in the decoding of P8 are already discarded, so that there may be encountered a distortion of the image or an interruption of decoding in the frames P8 to P14 until the frame I1 of intraframe encoding is decoded.